Yes, the hard drive can be replaced. I replaced mine instantly with a Samsung SSD, and put the original HDD in the place of the optical disk drive (with an adapter).
I'm not sure about the memory, [ftp://ftp.dell.com/Manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-15-3537_Reference%20Guide2_en-us.pdf|the official specification] says 8GB maximum, but [http://www.crucial.com/store/listparts.aspx?model=Inspiron%2015%20(3537)&Cat=RAM|the memory advisor on Crucial's website] recommends 16GB.